Have installed Thunderbird on an IMAC computer. From day one Thunderbird has been slow to open. Message box appears asking me to enter Login password. Sometimes doesn't accept password. Have to retype password again. Without warning, password rejected. My internet provider, Uniserve, gave me a temporary password for Thunderbird. Created a new password for Uniserve Webmail and Thunderbird. Worked for a while. No problem receiving and sending e-mails. This morning my new Thunderbird password is being rejected. What could be the problem?